1. Field of the Invention
The present invention relates to a time information acquiring apparatus which acquires time information with consistency from a time code signal included in a standard radio wave (standard time and frequency signal), and to a radio-controlled timepiece including the time information acquiring apparatus.
2. Description of the Related Art
Conventionally, there is known, for example, according to Japanese Patent Application Laid-open Publication No. 2002-286882, an apparatus which decodes a time code signal included in the standard radio wave so as to generate time information, the apparatus in which a plurality of pieces of time information is generated from a plurality of frames of the time code signal, and a consistency check is performed on the generated time information.
Currently, in order to acquire more accurate time information even under a poor reception environment, inventors including the inventor of the present invention develop technologies for decoding, the technologies by which a time code signal is not decoded frame by frame, but decoded by combining detection data of a plurality of frames thereof in order to perform a code determination.
However, for example, when a decoding process is performed by receiving three frames (the first to the third frames) of a time code signal under reception environments where the noise levels of the three frames thereof are the same and where the noise level of one frame thereof is higher than the noise levels of the other two frames thereof, the accuracy of the generated time information varies depending on a decoding method.
In the following, the first time information acquired by decoding a time code signal by using only the first frame thereof, the second time information acquired by decoding the time code signal by using only the second frame thereof, the third time information acquired by decoding the time code signal by using only the third frame thereof, the fourth time information acquired by decoding the time code signal by combining the first frame thereof with the second frame thereof, and the fifth time information acquired by decoding the time code signal by combining the second frame thereof and the third frame thereof are compared with one another.
When the noise levels of the three frames of the time code signal are the same, the accuracy of the five time information is as follows:
the first time information≈the second time information≈the third time information;
each of the first to the third time information<each of the fourth and the fifth time information; and
the fourth time information≈the fifth time information.
On the other hand, when much noise temporarily enters into the time code signal, and hence the noise level of the second frame thereof is higher than the noise levels of the other frames, the accuracy of the five time information is as follows;
each of the second, the fourth, and the fifth time information<each of the first and the third time information.
That is, although the fourth and the fifth time information are acquired by decoding the time code signal by combining the detection data of two frames of the time code signal, because the second frame which includes much noise is used as a material of the fourth and the fifth time information, the accuracy of the fourth and the fifth time information is lower than the accuracy of the first and the third time information each of which is acquired by decoding the time code signal by using only one frame thereof including less noise.
In other words, the accuracy of the time information acquired by a decoding method and the accuracy of the time information acquired by another decoding method may be reversed depending on a situation. Therefore, it is considered that, by using a plurality of types of decoding methods with a plurality of types of methods of a consistency check, more accurate time information can be acquired, even in a case where each of the time information is generated from a same number of frames of a time code signal.
The present invention provides a time information acquiring apparatus and a radio-controlled timepiece which can acquire more accurate time information having consistency by using a plurality of types of decoding processes with a plurality of types of consistency checking processes.